The research proposed is aimed toward understanding genetic recombination in a model eucaryotic system, Saccharomyces cerevisiae (yeast). The work involves the isolation of mutants which generally affect meiotic and mitotic recombination. Revertants of known recombination mutations will also be isolated (i.e., rad50-1, rad52-1, and reml-2). Both newly isolated and existing recombination mutations will be analyzed for their effects on recombination and interactions with each other. The properties of recombination, such as the distribution of recombination events along the chromosome, will also be analyzed in wild type strains. The RAD50, RAD52, and REM1 gene sequences will be isolated by genetic engineering techniques. The cloned genes will be used to study the control of transcription, to obtain overproduction of the gene product, and to perform in vitro mutagenesis. The latter will help to construct a fine structure map which can be correlated to function. Finally, the biochemical phenotypes of the recombination mutations will be investigated. Reml mutant strains will be examined for nicks and gaps in their DNA, and for loss of likely enzymatic activities; Rec minus mutants will be examined for loss of activity in an assay designed to measure early events in recombination. The genetic analysis of recombination genes will be correlated with their biochemical properties to construct an outline of the molecular events occuring in genetic recombination.